ASE A1 Engine RepairLubrication and Cooling SystemsEasy
A technician is performing a routine oil change on a vehicle. Upon draining the engine oil, the technician notices a significant amount of milky, frothy oil. What is the most likely cause of this condition?
- AOver-torqued oil filter
- BExcessive oil oxidation
- CUsing the wrong viscosity oil
- DCoolant contamination in the oil
Show answer & explanationAnswer & explanation
Correct answer: D. Coolant contamination in the oil
Milky, frothy oil is a classic indicator of coolant mixing with the engine oil. This usually points to an internal leak, such as a blown head gasket or cracked engine block/head.
Why the other options are wrong
- A. An over-torqued oil filter typically causes leaks or damage to the filter itself, not milky oil.
- B. Excessive oil oxidation leads to dark, thick oil, but not typically milky or frothy.
- C. Using the wrong viscosity oil can affect lubrication and engine wear but does not cause milky, frothy oil.
Milky Oil
Engine oil that appears milky or frothy, indicating the presence of coolant mixed with the oil.
- Caused by internal coolant leaks (e.g., head gasket, cracked block/head).
- Reduces oil's lubricating properties.
- Can lead to severe engine damage if not addressed.
Memory trick: Milky oil means water's in the soil.